Posted
by
kdawson
on Wednesday November 12, 2008 @01:45PM
from the my-kingdom-for-a-sunbeam dept.

Riding with Robots writes "Just days after announcing that the Mars Phoenix Lander has met its icy demise, NASA reports that a dust storm has left the rover Spirit on the edge of power failure. During one recent Martian day, the robotic geologist's solar array produced only 89 watt hours of energy, the lowest output by either rover in their nearly five years on Mars. Mission managers are taking steps to protect the hardy, battle-worn spacecraft, but the agency describes Spirit's status as 'vulnerable.'"

It would be very sad to see Spirit run out of power, but honestly, both the rovers have performed so far beyond their original expectations, it's astounding. I seem to recall they were originally meant for something like a two-month mission...four years ago.

So if we do lose Spirit soon, for my part, I think we can be satisfied with what it's already accomplished.

Both rovers were designed for a 90 Mars day (sol) mission. The difference between Earth days and Mars days is that sols are 24.6 hours long. Opportunity is on Sol 1710 or so and Spirit is on Sol 1730. Both rovers have lasted almost 20 times longer than originally designed.

The various components were designed to work no matter what they experienced for 90 days on the Martian surface.

I suspect that they were designed for the worst possible set of circumstances for 90 days which has allowed them to operate for the much longer time in the actual environment which is more benign than the worst case scenario.

Regardless of the semantics of the 90 days, the time the two robots have been operating is still an amazing achievement and everybody involved should be very proud.

They were indeed designed to work for almost the worst conditions expected for 90 days, based on what prior landers saw. If you read Dr. Steven Squyre's book Roving Mars (which I highly recommend for any space nerd, even though he wrote it several years too early), he describes at several points how worried they were that dust accumulation was going to kill these things before 90 days were up.

After talking about wipers, blowers, vibrators, etc. they concluded the best course of action was to just size the panels to produce the minimum required amount of electricity for operations after 90 days of worst-case dust accumulation. An added bonus of this approach was plenty of power to play around with early in the mission (and part of why they've done so well now). Accomplishing this ended up being a huge problem, however, and I think the power team spent weeks trying to figure out a geometery that would provide the needed amount of surface area, but not get in the way of all the other parts while folding down small enough to fit inside the tetrahedral lander platform. They finally got a break when they figured out a set of winglet-like tabs that unfolded from the back of an already folded section of panel.

The result didn't just solve the problem, it looked freaking awesome. Earlier renders of the rovers had them being nearly square or hexagon shaped, as opposed to the swept-back fighter wing look [seds.org] they have as built. Heck, Steve Jobs is probably even jealous of how sexy the MER's look, and they aren't even trying.

I got modded "troll" once for calling them that once, but the fact is they were designed for six month's use. They've been rolling around Mars for five years now. That's like an automobile with a ten year warrantee still running after fifty years without maintenance - in other words, a hooptie. It's not a slam, in this case it's a compliment.

I wish the guys who engineered the rovers would engineer cars. The rovers are simply amazing.

It would be very sad to see Spirit run out of power, but honestly, both the rovers have performed so far beyond their original expectations, it's astounding

Here's the things one or both rovers have survived so far:

* Full flash memory* Non-rotating wheel* Dusty solar panels* Stuck in dust dunes* Two winters (very cold)* Going down and up steep crater slopes* A global dust-storm that put power at the edge (about a year ago)* Broken joint motor* Power leak

That's nine. If they follow feline conventions, then number 10 will be it.

Isn't this just an effect of reduced sunlight during winter? Or is Spirit near the equator / other hemisphere? I know the Phoenix shutdown is at least partly due to seasonal changes

From the Press Release:

"NASA's Phoenix Mars Lander has ceased communicationsafter operating for more than five months. As anticipated, seasonaldecline in sunshine at the robot's arctic landing site is notproviding enough sunlight for the solar arrays to collect the powernecessary to charge batteries that operate the lander's instruments."

Or is Spirit near the equator / other hemisphere? I know the Phoenix shutdown is at least partly due to seasonal changes

Much closer to equator with a combination of winter (expected), dust storm (happens) and wear (by now) ganging up on it but it's in a "survivable" range. Phoenix was sent to the arctic region and never expected to survive winter AFAIK.

Isn't this just an effect of reduced sunlight during winter? Or is Spirit near the equator / other hemisphere? I know the Phoenix shutdown is at least partly due to seasonal changes

Time of year plays into it, certainly; this would be less worrisome at the height of summer. But it's not quite the dead of winter, either (solstice was something like 150 sols ago), so it could be worse.

Spirit is a little farther from the equator than her twin sister, Opportunity, so winters hit her somewhat harder than they hit Opportunity anyway. (Phoenix is at something like 60 degrees N latitude -- much farther than either rover.) On top of that, she was pretty well dust-covered already, thanks to a previous dust storm and the regular old ongoing dust-deposition process -- dust was blocking about 70% of the light hitting her solar arrays before this storm hit.

It's possible for this to turn out to be good news. Dust storms are caused by (and, in a classic feedback loop, cause) high winds, so it's possible that the winds will actually clean Spirit off and she'll end up better than she was before. Keep your fingers crossed.

That's what never made sense to me. Seems like all it would take is a low voltage cutoff circuit that shuts off power to everything as long as the voltage is below a threshold voltage, and then when the power comes back on, it would boot back up. In fact, most modern battery technologies require such safety measures to prevent the battery charge from getting so low that the batteries won't take a charge (or the cells reverse polarity like NiCd batteries have a habit of doing). I guess there's still the i

I guess there's still the issue of whether the batteries will fail to operate if they get too cold....

Yes, that's exactly the problem, and not just for the batteries. The rovers and landers need power just to heat themselves so that their components don't get damaged by the cold. In TFA they even say they've already started sacrificing parts of Spirit to conserve power:

"Mission controllers are commanding Spirit to turn off some heaters, including one that protects a science instrument, the miniature therm

The problem is, they need to keep themselves warm. Once the internal heaters are powered off, the batteries and electronics freeze up. It's cold enough on Mars that the differential expansion rates of the chip dies and the substrates they're mounted on will crack the chips. Once that happens, they're done.

It's fall in the northern hemisphere of Mars where Phoenix is located, so it dying was entirely expected, and although it lasted longer than its mission, they were hoping to get a few more weeks out of it. Landing was just a month before the summer solstice, so it had 30 days of conditions that started good and improved, then 130 days of declining conditions. Since it's in the arctic circle, it had complete daylight until a month or two ago, when the sun started setting again.

Spirit and Opportunity, however, are in the southern hemisphere, and it's early spring.
Between the dust on Spirit's solar panels and being about 12 degrees further from the equator than Opportunity, things got a little worrisome for Spirit over the winter, but her minimum power levels at that time were over twice the 89 Watt-hours quoted in the article.

Low power is slightly less of a concern now than it was then, because the surface temperature should be higher and so electronics should need less heating, but that huge drop in power is probably more than enough to make up the difference. The other potential positive factor is Spirit's batteries had a decent level of charge when the storm started, so if the storm dissipates quickly they'll probably be in the clear. Trying to maintain 89 W-hr for several months, however, could very easily be fatal, so they're trying to use an absolute minimum of power to keep her out of fault mode.

Spirit actually hadn't moved an inch for several months to save power until a week or two ago. Her team had parked her on a sloped rock face at about a 30 degree angle to square her solar panels to the noon sun over the winter, and because of relatively clear skies, she was even able to take a high resolution panorama [nasa.gov] (link is to an index, not directly to the giant 42 MB image) and do some stationary science. As the sun angle increased, they had just started inching back towards a 20 degree tilt to follow it when the dust storm hit. There's a rather dramatic picture of what that 30 degree tilt [nasa.gov] looks like on the program site.

As of the last report I've seen, the atmosphere is 69% opaque due to suspended dust (although I believe more than 31% of the sunlight diffuses through indirectly), and the dust coating on Spirit's solar panels is only letting through 32% of of the sunlight that actually reaches them. In the past they'd had good luck with winds cleaning the panels off, but that hasn't happened in a while. The team is hoping that the same seasonal weather that brings on these dust storms will generate a few lucky dust devils.

Opportunity, on the other side of the planet meanwhile, has been getting 500-600 Watt-hours and averaging about 50 meters per day of progress towards the huge crater Endeavor, which is 12 km away.

And what nutjob modded the parent as a troll? Sheesh! And to think we probably let that person vote, too.

The phoenix lander was near the north pole. It was there checking for ice. The phoenix lander being in the colder region will actually be so cold it will have carbon dioxide freezing onto it. Its unlikely to wake back up in the spring...but possible.

The cool thing with the phoenix lander is it DID find ice and even saw snow.

This was thought about, and discarded. While on the surface it seems like a good idea, in actuality it's incredibly difficult to implement, since the dust on Mar's is so 'sticky' - from what I've read elsewhere, the electrostatic charge of the dust on Mars is very high, and any attempt to scrape it off the solar panels would just move it around, not really remove it.

Besides, with a two month life expectancy, I think it was determined that they wouldn't need to remove any dust from the solar panels since the rovers would have long since died...

Besides, with a two month life expectancy, I think it was determined that they wouldn't need to remove any dust from the solar panels since the rovers would have long since died...

Well, if I remember correctly, it was dust accumulation itself that was supposed to limit the life span to 90 days, not failure of any component. They didn't know that the Martian wind would do a decent job of cleaning the panels by itself, so they determined that was how long until the rover couldn't power itself any more.

thin plastic that can be pulled off like motorcycle racers use would have worked.

Also any adhesive system would have to survive the long trip in space and the extreme cold of Mars. Currently the rovers need heaters during night to ensure the electronics survive. I don't think any adhesives would last.

The dust is super clingy due to static. So a blower would have to be powerful. Equipping a powerful blower would mean sacrificing other things due to weight and space limitation and may not be practical.

Things that work here on Earth in temperate conditions may not work on Mars. Mars has incredible temperature swings: extremely cold at -190 Farenheit and up to 77 Farenheit in the same day. Most blowers/fans here on earth could not survive such conditions due to their moving parts

NASA probably thought of that, but the issue is how practical any wiper system would be. Unlike automobile wipers, there's no air or water supply to remove the dust. Adding a system to compress air would have added unacceptable weight to the rover and every little bit counts (even if would work reliably under Mars conditions). A water system would have been out of the question. A waterless/airless system then depends on the material you would use. Such a material would have be softer than the panels or they would damage them; however, a softer material (rubber, polypropylene, polyethylene) probably would not survive the extreme conditions of Mars.

And that's just the survivability aspects. Now factoring the usability aspects: Some sort of arm would have to be long enough to reach all the panels. None of the rovers arms can extend that far so they would have to have been modified. This might add weight and complexity.

Probably the biggest reason why NASA didn't put one in was the rovers were designed for 90 sol missions. Having them last 5 years is a bonus. Along the way, the Rover team has dealt with the problems that have come with extending the mission beyond the original parameters: wheels no longer work, tools no longer function, dust storms limit power usage, etc. This is one issue that they knew would eventually cause the rovers to cease functioning after a few years.

Pardon my ignorance, but I couldn't help but notice the horizontal positioning of the panels. Is there a reason (such as angle of the sun) why there weren't at least some panels positioned at a sloping angle to allow dust to slide off? Or is the dust too sticky for it to make a difference?

Having the panels horizontal probably generates the maximum solar conversion of any position. If some panels were tilted, they would not always generate the maximum depending on where the Sun was positioned. That is unless the panels could change positions. That would have make the rovers a lot more complicated and they were already pretty complicated. Also having them at an angle would not help. The dust is very clingy due to electrostatic forces. At this point, NASA is probably hoping for dust devils

Probably the biggest reason why NASA didn't put one in was the rovers were designed for 90 sol missions. Having them last 5 years is a bonus

Yes, people don't tend to realize the cost and redundancy required to design a mission to last for years on another planet. Basically every such mission is designed for 90 days or less and you hope to get a lot more.

So, it's just a matter of waiting, if Spirit runs out of power, no big deal, it will stop working, and then if it gets cleaned, it will come back again.

If the batteries are completely drained, Spirit will probably never run again. Both rovers need a certain amount of power to run their heaters. The heaters keep the sensitive electronics from freezing. The loss of power means that the loss of the electronics. During the previous dust storm, the rovers were put into power save mode to outlast the storms.

Hmm... the only constant I see there is that the equipment with names that are based on motivational posters are still going.

Novelty poster publisher Despair, Inc. today announced a surprise entry in to the unmanned space probe arena. A spokesperson for the company commented, "NASA pretty much threw down the gauntlet with all those names."

Represenatives for the company went on to say that their first probe had already been named. "It's called Apathy. We've already began production." When pressed for details, the company spokesperson continued to note that "...actual construction of the probe has halted as neither the design team nor the construction crew could be bothered to finish it. Operations has decided that if they can't be given a finished probe, well, there's just no reason to even bother thinking about a launch and have scrubbed any additional work on Apathy." The spokesperson went on to proudly announce that Despair had already achieved their first non-launch to date and are eagerly looking forward to their program's next success.

Your bare listing of their fates obscures one important point - each and every one of those missions exceeded their design lifetimes. Even Phoenix, which was designed to last only three months, survived nearly five months.

I only included the status to let people know the status. Yes, we all know that they've exceeded their expected life spans. I also didn't include dates. It's just a simple damned list of successful Mars landers.

Spirit, Pathfinder, Opportunity, Sojourner, Phoenix, Viking... most people remember Spirit and Opportunity, and associate all others as "another Mars rover".

3. Fire a kazillajoule laser at Mars to energize the solar panels. This is actually the least worst idea so far which is depressing.

4. Spend the remaining energy teaching the rover to do the Hammer Dance with it's eight independently swiveling wheels. If you got to go down, go down doing the Hammer Dance that's what I always say which is maybe why nobody sits with me in the cafeteria.

4. Spend the remaining energy teaching the rover to do the Hammer Dance with it's eight independently swiveling wheels. If you got to go down, go down doing the Hammer Dance that's what I always say which is maybe why nobody sits with me in the cafeteria.

4. Spend the remaining energy teaching the rover to do the Hammer Dance with it's eight independently swiveling wheels. If you got to go down, go down doing the Hammer Dance that's what I always say which is maybe why nobody sits with me in the cafeteria.

approach to Rover problems. Your idea will not work. Here is why it won't work. (One or more of the following may apply to your particular idea, and it may have other flaws which used to vary from planet to planet before a bad solar system law was passed.)

(X) It requires too much power
( ) It may make situation worse
( ) It doesn't solve the problem
(X) It works here on Earth but not on Mars
( ) It will work for two weeks and then it might get stuck
( ) It does not account for the climate of Mars
(X) Marvin the Martian will not put up with it

( ) Sorry dude, but I don't think it would work.
(X) This is a stupid idea, and you're a stupid person for suggesting it.
( ) Nice try, assh0le! I'm going to find out where you live and burn your
house down!

4. Spend the remaining energy teaching the rover to do the Hammer Dance with it's eight independently swiveling wheels. If you got to go down, go down doing the Hammer Dance that's what I always say which is maybe why nobody sits with me in the cafeteria.

I once knew a street walker who said that, and well, let's just say she didn't have a large clientèle.

Well, I had read about the fear of issues with dust settling on the solar cells; I figured they should have used the same mechanism that NASCAR uses to clear the lenses of the car-cams. A clear, celluloid cover over the cells, which can be rolled-up off of a spool on either side of the cells, and a brush along the top of the spool. Every time dust collects on the cells, the spool winds out a new clear celluloid cover, the dusty bit is brushed off, and rolled up. Next time, the motor rolls the opposite direction.

The most Illustrious Council of Elders has issued an update following yesterday's Planetary Day of Celebration [slashdot.org] of Victory over the Northern Invader. K'breel, Speaker for the Council, spake thus:

Rejoice! One mechanical nightmare from the evil blue planet has fallen silent. The other robotic terror stirs, but only because it in quivers in fear, for we have darkened the skies with the ashes of its bretheren. We shall starve the invaders of light -- there shall be no mercy for them, as the day shall soon come when our planet itself shall rise to entomb them in a cloak of red dust! On the Tracks of the Founders, this we swear!

When a newly-hired journalism intern implied a correlation between the invaders' movements and seasonal weather patterns, and pointed out that that the current sandstorm had begun to abate, and that the same winds that were promised to bury invaders in dust could also, on occasion, blow accumulated dust off the invaders, K'Breel, in a rare display of compassion, responded by offering him a piece of jerky made from the dried gelsacs of a recently-retired member of the Press Corps.

It's a funny thing...these little machines have done the job they were designed and built to do, done it well, and while I know they're expensive versions of RC cars, there's a part of me that will be sad when they stop working.

Spirit has not been moving much recently - I believe that since 2007 it has only gone about 1 or 2 meters. It's not just the power, it's also the crippled wheel.

What the spacecraft needs is a few dust-devils to blow the dust off. The original mission plan assumed that both rovers would suffer power failures after a few months due to dust, and people were pleasantly surprised to have the dust cleared off by the dust-devils. Why this is no longer working is unclear, at least to me - the climate may be changi

During a day, solar panels don't produce any watts of energy. Watts are a compound unit, specifically joules per second. Joules are a measurement of energy, and what would be produced in a a time period. Watts represent the instantaneous rate of power generation.

This has been covered before... Anyway, here's the deal: 1.) The wiper would add weight and cost. 2.) The wiper would require power. 3.) The wiper would eventually wear out. 4.) The wiper might get stuck mid-"wipe", blocking the solar energy incident on the panels. 5.) The wiper would scratch the surface of the solar panel, reducing the amount of absorbed light. Either 4 or 5 would reduce the amount of power generated.